<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
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  <title>Document</title>
  <style>
    div {
      width: 400px;
      height: 400px;
      /* 默认值为透明，即：transparent或者rgba(0, 0, 0, 0) */
      background-color: rebeccapurple;
    }
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</head>
<body>
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